techie parabola question

[HoneySuckleDreams]

hello

We have a Lenson 80cm dish with the original LNB. My friend has donated a Quad LNB he no longer needs but was supplied by Sky. I've tried replacing the LNB on the dish to the donated one but get a big change in strength/quality. My guess is that the SKY LNB's are built to cope with the elliptical dishes, whilst the Lenson dish is circular, which is why i'm getting a duff signal. Is this thinking correct? Should I shelve out for a Quad Lenson LNB?

Thanks for any help

 

[AnOther]

The Sky elliptical dish is only a section of a full parabola so the profile should be the same.

I've heard somewhere that some Sky supplied LNB's don't need skew, just a thought.

[Anton Redman II]

How have you overcome the the neck of the Quad LNB being smaller than the standard LNB ?

It is possible the extra weight of the quad has caused the arm to droop slight and you may be able to improved signal quality by fine tuning the alignment.

[HoneySuckleDreams]

Anton: The neck is a bit smaller but you can pack out the clasp with bits of old inner tube. I think the dish might need realigning a bit because of the weight. I'm going to see if I can buy an actual proper fitting, they come with an inbuilt level as well I think.

Another: The actual LNB sensor bit has a skew already, so it looks like i don't need to fiddle too much with that.

It seems to be a bit hit and miss at the moment with the signals anyway with the current LNB. I can get 90% strengh 100% quality for BBC1 HD but only 60%/20% for RADIO4LW (the HUMAX gives a much better insight into the signal strength/quality when you switch channels than the old SKY box)

Looks like I will be up on the roof again at the weekend.... maybe I will wait until England are knocked out of the World Cup and Murray out of Wimbledon before I try to fiddle too much.

[AnOther]

[quote user="crazyfrog"]I can get 90% strengh 100% quality for BBC1 HD[/quote]Pretty well exonerates the LNB then [;-)]

Footy and tennis seem to present the ideal opportunity to fiddle about without missing much [:P]

[HoneySuckleDreams]

Another: I think you misunderstood. The current single LNB gives a good signal, but only on certain channels. The donated Quad LNB doesn't give a good signal even on those the current LNB is strong on.

I'm still away working at the moment, but when I get home I'll try the Quad with no skew and see if that helps.

[gyn_paul]

The other thing to consider is the distance from the neck of the LNBs to the face.. are they the same? If not it may be sitting sightly ahead or behind the prime focus spot (OK, OK, I know you can't actually have a prime focus spot on an eliptical dish... but you know what I mean !).

p

[HoneySuckleDreams]

good point....

The more I think about it, I think matching the LNB to the dish is of primary importance. I think I will be looking into getting a Lenson Quad LNB

[Anton Redman II]

[quote user="gyn_paul"]

The other thing to consider is the distance from the neck of the LNBs to the face.. are they the same? If not it may be sitting sightly ahead or behind the prime focus spot (OK, OK, I know you can't actually have a prime focus spot on an eliptical dish... but you know what I mean !).

p

[/quote]

The dish may be oval ( taller than it is wide or vice versa ) but it remains parabolic so it does have a prime focus but it must be almost 40n years since I learnt about conic sections.

I think an LNB to fit the dish is the way to go but if the dish is easy to get at you might try moving the LNB marginally in or out. ideally with a receiver which shows signal strength and quality for the channel you are watching